The present invention relates to a packing container for pressurized contents.
Packing containers of the non-returnable type for pressurized contents, e.g. beer or carbonated beverages, are considerably more complex and expensive than packing containers for non-pressurized contents, e.g. juice or milk. This is due not only to the different and higher demands that are made on the capacity of the packing containers for pressurized contents to withstand an internal pressure, but also to the demand for a very high gastightness made on the material of which the packing containers are made. Whereas packing containers for non-pressurized contents can be manufactured simply at the same time as they are filled and can be given a simple tetrahedral or cushion-like shape, pressurized packing containers, because of the difficulty of finding an acceptable material which fulfills both the demands of mechanical strength and of high gastightness. Containers for pressurized contents must be given a complicated shape and must be manufactured from several different materials, e.g. a plastic and aluminium laminate so as to obtain the desired gas tightness, and a fibrous material arranged on the outside in order to ensure the required mechanical strength.
A known package of this type thus consists of a liquid-and gastight container of plastic material, which is surrounded for the most part by a casing of laminated paper material. While the free end parts of the liquid-tight container, because of the high internal pressure, must be made of thick plastic material, the remaining part of the container, that is to say the part of the container which is surrounded by the laminated casing, may be made of thin plastics, since the casing takes up the pressure loads caused by the contents and relieves the container wall. This brings about a certain economy in material, but the packing container thus configured becomes relatively complicated in its design and manufacture.
It would be desirable therefore to have a packing container for pressurized contents which is as simple as possible in its shape, and which is uncomplicated and economical with regard to material in its design. These requirements are met to a high degree by a cushion-shaped packing container, but it has not been possible up to now to impart to such a packing container sufficient mechanical strength so as to withstand the possible internal pressure.
It is an object of the present invention to provide a packing container for pressurized contents which does not have the disadvantages of the previously known packing containers and which makes use in an optimum manner of the materials from which it is made.
It is a further object of the present invention to provide a packing container for pressurized contents which, in spite of fulfilling the demands made with regard to tightness and strength, is of a design which is economical in respect of materials and of cost.
These and other objects have been achieved in accordance with the invention in that a packing container for pressurized contents comprising a liquid-tight container with two sealing fins situated at a distance from each other, which are folded down against the outside of the container, are joined together by means of an external strengthening element.
Preferred embodiments of the packing container in accordance with the invention have been given the further characteristics described in detail below.
By shaping the liquid-tight container from a flexible tube which on both its ends is flattened and sealed together to form mutually parallel sealing fins, a container of uncomplicated cushion-form is obtained for which a minimum of material is consumed. The walls of the packing container, without any difficulty, tolerate high internal pressure loads, but the sealing fins formed at the ends of the cushion require some form a strengthening in order to permit an equally high internal pressure as the remaining parts of the container. This strengthening is achieved in accordance with the invention in that the sealing fins are folded down against the outside of the container and are mutually joined by means of an external strengthening element which is attached to the outside of each fin when it is in folded down position. The elongated strengthening element, which is in the shape of a band, thus serves to absorb tensile stress and extends along the whole of one side of the container. It may be said that the strengthening element primarily fulfils two functions, namely in the first place the holding down of the sealing fins of the container in contact against the outside of the seals, and secondly the taking up of a large part of the stresses which are caused by the internal pressure.
The present invention also relates to a method of manufacture of a packing container for pressurized contents. Earlier known packing containers for pressurized contents, as mentioned previously, were usually made of several parts, namely an inner container and an outer strengthening casing for the greater part surrounding the same. The manufacture of these packing containers must necessarily be complicated, since it has to be done in several steps with assembly between the steps. The finished packing container is filled subsequently in a separated working phase and capped.
It would be desirable to simplify this method of manufacture and to provide a packing container which can be manufactured while being filled at the same time, so that the majority of the working phases required previously become unnecessary.
It is an object of the present invention, therefore, to provide a method for the manufacture of a packing container for pressurized contents which does not have the disadvantages of previously known methods of manufacture.
It is a further object of the present invention to provide a method for the manufacture of a packing container for pressurized contents, which method is suitable for automatic manufacture.
These and other objects have been achieved in accordance with the invention in which a method for the manufacture of packing containers for pressurized contents includes sealing off a tube filled with contents in transverse zones so as to form cushion-shaped containers with sealing fins situated at a distance from each other. The sealing fins are folded down against the outside of the container and are then retained in this position by means of a strengthening element which is applied to the outside of the container.
Preferred embodiments of the method in accordance with the invention have been given further characteristics as described in detail below.
The method in accordance with the invention makes it possible to continuously manufacture cushion-shaped containers from a tube filled with contents. By making use of a multiparts strengthening element each of the sealing fins can be joined to the respective part of the strengthening element while the fin is still in its original position, disposed substantially axially with the packing container. This facilitates the sealing between the fin and the strengthening device and makes it possible moreover, prior to the ultimate connecting together of the two parts of the strengthening element, to adapt the length of the strengthening element accurately in such a manner that in its effective position it fits well against the outside of the container and takes up the stresses caused by the internal pressure.
The packing container in accordance with the invention and the method for the manufacture of the same will now be described in more detail with special reference to the enclosed drawing which schematically shows two embodiments of a packing container in accordance with the invention.